A. Field of the Invention
The present invention relates to a light-emitting diode (LED) device and the method of manufacturing the same. More particularly, the present invention relates to an LED device, made of GaN-based compound semiconductor materials, whose sidewalls and bottom surface are both covered with a conductive layer, and the method of manufacturing the same.
B. Description of the Related Art
In recent years, the GaN-based compound semiconductor has received more and more attention to use of a material for manufacturing blue, green, blue-green light-emitting devices, such as blue LEDs or blue laser diodes (LDs). The blue LED, for example, generally has a structure including at least one n-type GaN-based compound semiconductor layer, an active layer made of an intrinsic or doped GaN-based compound semiconductor material, and at least one p-type GaN-based compound semiconductor layer, which are sequentially laminated on a substrate.
In manufacturing the conventional blue LED, transparent sapphire is usually used as a material of the substrate of the blue LED. Different from the semiconductor substrate used for other semiconductor light-emitting devices, sapphire is an electrically insulating material. Consequently, it is impossible to directly form the n-type electrode on the sapphire substrate. As a solution to this problem, the n-type GaN-based compound semiconductor layer is partially exposed by means of etching the blue LED so as to provide a conductive surface where an n-type electrode is effectively to be formed.
Referring to FIG. 1 for a more specific understanding of the conventional blue LED described above, the conventional blue LED mainly includes a sapphire substrate 101, an n-type GaN-based compound semiconductor layer 102, an active layer 103 made of an intrinsic or doped GaN-based compound semiconductor material, and a p-type GaN-based compound semiconductor layer 104. As described above, an n-type electrode 105 is formed on the exposed surface of the n-type GaN-based compound semiconductor layer 102, while a p-type electrode 106 is formed on the p-type GaN-based compound semiconductor layer 104.
The conventional blue LED shown in FIG. 1, however, has several disadvantages as described in the following. First of all, the insulating sapphire substrate 101 of the blue LED fails to form an electrical connection with a cup-type lead frame 107 when mounted on the surface of the cup-type lead frame 107. In order to electrically connect the blue LED with the cup-type lead frame 107, it is necessary to use a metal bonding wire 108 for electrically bonding the n-type electrode 105 to the surface of the cup-type lead frame 107, as shown in FIG. 2. Since another metal bonding wire 109 needs to electrically bond the p-type electrode 106. to a separate lead frame 110, the wire bonding process must be performed twice for completely bonding the conventional blue LED. In addition, the metal bonding wire 109 is bonded on the p-type electrode 106 preferably through a bonding pad 111. As a result of the two-wire-bonding characteristic, the complication of the conventional process of manufacturing the blue LED and the die size of the blue LED are both greatly increased, which result in a high fabrication cost.
Moreover, the structure and arrangement of the electrodes 105, 106 of the conventional blue LED is asymmetric as shown in FIG. 3, which is the top view of the blue LED shown in FIG. 1. As a result, the electric current in the conventional blue LED does not flow in a symmetric and top-down direction. Therefore, it is very difficult for the conventional blue LED to achieve a uniform A current spreading characteristic. Since the current spreading characteristic is non-uniform, several high current density points exist in the conventional blue LED, which are easily damaged during the operation.
Furthermore, the well-known electrostatic discharge (ESD) problem inevitably occurs in the insulating sapphire substrate 101. The above-mentioned disadvantages greatly reduce the performance and reliability of the conventional blue LED.
Accordingly, it is desirable to provide a blue LED that achieves a one-wire-bonding characteristic without greatly increasing the complication of the manufacturing process and the fabrication cost. It is also desirable to provide a blue LED that achieves a uniform current spreading characteristic and is free from the ESD problem. Furthermore, it is desirable to provide a blue LED provided with a mirror-like reflector formed on its bottom surface, thereby increasing the light-emitting efficiency of the blue LED.